How can I insert a line?

You can use the Form Separator widget to insert a line in your form.
http://widgets.jotform.com/widget/form_separators

This is how the form will look after. 

You can check out this demo so you can see the form separator in action: https://form.jotform.com/60888846874983 

If you need further assistance, do let us know.
Regards.